Electron beam tube



Aug 18, 1942. c, THQMPSQN v 2,293,417

ELECTRON BEAM TUBE Filed July 27, 1940 INPUT L.Wfil

1mm 12 g ,/4i"- I I Q l I w OSCILLATOR .9 l 4 s g I 8 \l a "0, I

our ur INVENTOR HARE Y C. THOMPSON A TTORNE Y Eatented mg. 18, 1942 EEEc'raoN BEAM rune Harry 0. Thompson, Lndlow, Vt, assignor to Radio Corporation of America, a corporation of Delaware Application July 27, 1940, Serial No. 347,835

7 filaims.

My invention relates to electron discharge devices having thermionic cathodes and cooperating cold electrodes and more particularly to devices of this type which utilize an electron discharge concentrated into a more or less well defined beam or beams of electrons and which will operate at the comparatively low voltages generally used in the conventional receiving tube.

The present application is directed to a beam tube of the type disclosed in my copending application, Serial No. 232,805 filed October 1, 1938, and assigned to the RCA Manufacturing Company, Inc.

The tube described in that application comprises essentially a pair of concentric coaxial tubular electrodes and positioned between them a cathode and control grid for supplying electrons. A screen electrode surrounds the cathode and control grid and is provided with oppositely disposed apertures for directing a pair of oppositely disposed electron beams along curved paths between the two tubular electrodes toward an intercepting or output electrode. The inner of the two tubular electrodes is provided with radial extending members each having an aperture or a second electrode enclosing the output or collector electrode and provided with apertures through which the beams can be directed onto the output electrode. Although either of the two tubular electrodes could be used as a control electrode,

beam focus is affected when the beam is deflected by the deflecting electrodes. In order to accommodate the electrode system the tube envelope must be of some length and sometimes of an odd shape.

It is an object of my invention to provide emcient electron discharge devices having desirable transconductance and impedance characteristics which are not obtainable with the conventional type of tube structure.

It is another object of my invention to provide a beam tube utilizing secondary emission amplification in which the secondary emitting surfaces are protected from the vaporized coatings of the cathode.

It is also an object of my invention to provide a beam tube utilizing deflecting electrodes in which the deflection sensitivity for the same overall tube dimensions is greater than in the types heretofore available and also to provide a. beam tube in which the beam focus is not me.- terially affected by the action of the deflecting electrodes.

Still another object of my invention is to provide an improved electron discharge device of the type'described which is of much the same the inner electrode has applied to it a varying potential for shifting the beams so as to pass through the apertures to the collector or output electrode or to one of the other electrodes in the tube, thereby controlling the output current. The present invention makes use of this type of tube in combination with other means including a secondary emitting surface for increasing the transconductance of this type of tube and providing advantages not present in conventional multipliers using a straight beam and secondary emitting surfaces.

While secondary electron emitting surfaces may be provided in combination with beam tubes for increasing the transconductancc of such tubes, where the conventional straight beam is used and where the secondary emitting surfaces are exposed directly to the cathode, material evaporated from the thermionic cathode may deposit on the secondary emitting surfaces causing a reduction of the emission from the secondary emitting surfaces. Further, where straight beams are directed between deflecting plates comparatively long beam paths are necessary to provide for deflection sensitivity and in tubes of this type the dimensions and is operated at much the same voltages as the conventional receiving tubes by segregating the space current into an electron beam or beams and controlling and utilizing the properties of the beam to advantage.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which thesingle figure shows a transverse section of an electron discharge device made according to my invention and its associated circuit.

In accordance with my invention I provide an envelope 9 containing a cathode It for supplying electrons, the cathode being surrounded by a shield and control grid H and a screen and beam forming electrode l2, these electrodes being coaxial. While only one beam is formed by the structure shown, it is obvious that two oppositely disposed beams could be formed and utilized. The control grid H is provided with a solid sheet backing ii to direct only a single beam from the cathode. The beam issuing from the opening it of electrode i2 is directed between a pair of concentric coaxial tubular members It and i5 and by the application of proper voltages the beam is made to travel a curved path as indicated by the dotted lines. Members l4 and I 5 also produce a focus or desired concentration of the beam at or near the aperture between elements l6 and I1.

Disposed approximately 180 removed from the cathode is a radially extending member or shielding element I6 extending from the tubular member l5. Adjacent this tubular member is an electrode H which provides for the secondary emission of electrons, these secondary electrons being released upon bombardment of the surface l8 of electrode l! by the beam following the curved paths between the tubular electrodes 14 and I5. These secondary electrons are captured by output electrode l9, this electrode being shielded by element i6 and electrode I'I. While the electrode I'l could be uncoated, it is preferable to coat the surface to increase the ratio of the secondary-to-primary electrons bombarding the surface l8 of electrode [1.

In the arrangement shown a signal voltage is applied to the control electrode ll for modulating the beam in a conventional manner and a second alternating voltage or oscillator voltage is applied to the inner tubular member I5 for deflecting the electron beam between the surfaces of the electrods I4 and 15. As indicated by the dotted lines marked a, b and c, the electron beam may be deflected between the positions shown to either strike extension IS on electrode [5, the surface i8 or the radially extending lip ll of electrode I1. The signal voltage is preferably applied by means of input circuit 20, the oscillator voltage by the oscillator circuit 2| and the output voltage applied to the output circuit 22 electrically connected between the output electrode l9 and the source of voltage supply 23. The electrode l5 exhibits a negative resistance characteristic so that the tube acts as a self-oscillator when circuit 21 is connected to the electrode l5. If desired, of course, the oscillator could be excited externally.

While shown used as a mixer tube in a superheterodyne circuit, my tube has other applications and could be used, for example, as a volume control tube, the volume control voltage being applied either to the inner tubular electrode i5 'or the outer tubular electrode I4.

Because of the longer travel of the beam between the two tubular electrodes I4 and [5, the control of the beam is more sensitive for tubes of given dimensions. The focus is not disturbed and because the secondary emitting electrodes are completely shielded geometrically by the peculiar formation of the electrodes used, any

material vaporized from the cathodeis received by the surfaces of the tubular electrodes and hence the surface of the secondary emitting electrode is well protected. Due to the position of the output electrodes with respect to the input, there is no interaction between the-input and output circuits and their connecting electrodes. Furthermore, because of the compact arrangement of the electrodes, envelopes of conventional shape and size can be used.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no departing from the scope of my invention as set forth in the appended claims.

What I claim as new is:

1. An electron discharge device including an envelope containing a cathode and a control electrode for said cathode, means forforming electrons from said cathode into a beam, means including a control electrode adjacent the path of the beam of electrons for causing said beam to travel along a curved path, a secondary emissive electrode positioned in the path of said beam for emitting secondary electrons when struck by said beam, and an electrode adjacent the secondary electron emitting electrode for receiving secondary electrons emitted by the secondary electron emitting electrode.

2. An electron discharge device including an envelope containing a cathode surrounded by a control grid, means for forming electrons from said cathode into a beam, an electrode in the path of said beam of electrons for causing said beam to travel along'a curved path, a secondary emissive electrode positioned in the path of said beam for emitting secondary electrons when struck by said beam and an electrode adjacent the secondary electron emitting electrode for receiving secondary electrons emitted by the secondary emitting electrode, a control electrode adjacent the path of said beam, said control electrode for shifting said beam whereby said beam may strike the secondary electron emitting electrode or some other electrode in said envelope.

3. An electron discharge device having an envelope enclosing a cathode, a control grid and screen electrode surrounding said cathode for controlling and forming electrons from said cathode into a beam, a pair of adjacent electrodes including a control electrode between which said beam is to be directed for causing the beam to travel along a curved path, the distance between I the cathode and first control electrode being short in comparison to the length of the curved path between the cathode and the pair of adjacent electrodes, and a secondary emissive electrode in the path of said beam of electrode for emitting secondary electrons when struck by said beam, and an electrode for collecting said secondary electrons and positioned outsid the path of said beam.

4. An electron discharge device including an envelope containing a cathode surrounded by a control grid and a screen electrode comprising a tubular electrode having an aperture for forming a beam of electrons, a pair of concentric tubular electrodes mounted adjacent the screen electrode the path of the beam of electrons being between the opposed surfaces of said tubular electrodes for causing said beam to travel a curved path, an electrode positioned in' the path of the beam to be bombarded by said beam for releasing secondary electrons, an auxiliary electrode adjacent said bombarded electrode for receiving secondary electrons emitted by the bombarded electrode, and a radially extending shield secured to the inner of the tubular electrodes for shielding the auxiliary electrode.

5. An electron discharge device including a pair of coaxial concentric tubular members, a cathode and a control grid for supplying electrons and positioned between said concentric tubular members and an electrode surrounding said cathode and control electrode for forming electrons from said cathode into a beam directed between the opposed surfaces of said tubular members, and an electrode positioned some dis tance removed from said cathode and between said tubular electrodes and in the path of the electron beam to be bombarded by said beam to release secondary electrons, a radially extending member connected to the. inner of said tubular members adjacent the electrode to be bombarded and an auxiliary electrode positioned adjacent the bombarded electrode but out of the path of the beam of electrons and on the opposite side of the radially extending member from the side facing the arriving electrons, said radially extending member shielding said auxiliary electrode.

6. An electron discharge device including an evacuated envelope containing a cathode for supplying electrons, and means for forming electrons from the cathode into a beam, 9. control electrode for said beam of electrons, an electrode positioned in the path of the beam and coated with emitting material for emitting secondary electrons when struck by said beam, and an output electrode adjacent the secondary electron emitting electrode and between said cathode and secondary emitting electrode for receiving secondary for said beam of electrons, means including a second control electrode adjacent the beam of electrons for deflecting said beam, an electrode positioned in the path of the beam and coated with emitting material for emitting secondary electrons when struck by said beam, and an output electrode adjacent the secondary electron emitting electrode and between said cathode and output electrode for receiving secondary electrons emitted by said secondary electron emitting electrode, said secondary emitting electrode and said output electrode having surfaces approaching each other in the direction of travel of the electron beam. HARRY C. THOMPSON. 

